In a system utilizing a camera to detect a person for door control, a shadow in a captured image needs to be removed. One shadow determination method involves applying a texture such as a lattice pattern to a background of an image capturing target and determining that a dark area in an input image where the background texture remains is a shadow. Another shadow determination method involves determining a shadow based on a brightness ratio of the background image and the input image.
However, the method using the background texture (background pattern) is not applicable if the pattern of the background is precluded from being freely set. The method is also not applicable if a low resolution of the camera prevents the background texture (background pattern) from being captured. In the method for comparing the brightness of the background image to the brightness of the input image is a dark area determines is as a shadow, and therefore a person in a dark cloth may be erroneously determined as a shadow.